In order to improve insulation levels of a high-voltage electrical appliance, such as a transformer bushing, a wall bushing, a cable terminal, a transformer, an insulated busbar and other capacitive insulating cores, a plurality of coaxial capacitive screens are generally used in an insulation structure to play a role of balancing an electric field, the innermost layer is connected to a high-voltage potential, and the outermost layer is connected to a low-voltage potential or a ground potential to form a capacitance voltage-sharing core with a plurality of capacitive screens in series.
For many years, the skilled in the art is trying to use this high-voltage capacitor to draw energy from the power grid, which is used as a power supply of low-voltage appliance, or replaces the voltage transformer to measure the high voltage, or detects an insulation state of the high-voltage electrical appliance, etc., thereby having larger effect in an intelligent power grid. However, the capacities of the capacitors in series are relatively small, i.e., epoxy resin can only reach 1000 to 1500 pF using as a medium, the drawn energy drown is small (tens of milliamps to hundred milliamps), is easy to be interfered by the electric field, and is difficult to meet the requirement above.